Four-stroke internal combustion engine having reduced noise emissions

Abstract: The present invention provides a four-stroke internal combustion engine having reduced noise emissions. The engine includes a filter element having substantially flat inlet and outlet sides, a first housing portion, and a second housing portion coupled to the first housing portion. The first and second housing portions define an air chamber in which the filter element is supported. The second housing portion includes an interior surface, at least one protrusion to space the inlet side of the filter element from the interior surface, and an air passageway. The outlet of the air passageway is positioned adjacent the interior surface to deliver air to the air chamber between the interior surface and the inlet side of the filter element. A ratio of the volume of the air chamber to the length of the air passageway is between about 5 in2 and about 20 in2. (end of abstract)